I, too, come from FF/DX and the nose-bleed ISOs with low noise and great IQ of the past few years. I also now shoot a lot with my pair of GX7 bodies, discreetly and quietly many times at ISO 3200 and even 6400 and higher when I push the sliders. They seem to consistently underexpose but is easily handled with ACR and noise its noise reduction. My normal master image size is 19x14 from this camera. I'm shooting in monasteries and churches and become a fly on the wall with the Panasonic bodies. Though the IQ isn't the same as that of my D800 and D3s bodies, the freedom from sticking out like a sore thumb is worthwhile trade-off for slightly lower technical quality.
Compared to my previous generation of cameras from a few years ago, the GX7 is better in low light, though not as good as contemporary DX/FX bodies. Is that a negative? If you need the best image quality, chase the brass ring and keep up the GAS. But if you can think pragmatically and think differently and change your expectations, stay the course with the GX7 and relish the possibilities.
However, I come from the "dark ages" of the 20th century where pushing Tri-X to ISO 1600 and 3M 1000T were the norm. Tri-X usually did a good job but it was still hit-and-miss and don't even ask about the 3M 1000T regarding captures and IQ... Many people who I know today seem to have issues about the noise of low-light shooting, even with their high-end cameras today. When I ask them if they ever shot film, the answer is generally no. Also, few go beyond a web posting, let alone print from the files.
I do print from my files and am very content with the files from the GX7, mostly shot with slow zoom lenses and under terrible light at high ISOs, 3200 and up. With good craft, good editing and careful post processing of the raw files, I easily get master files that print easily at 16x20. One image I now have on the wall is a 30x40 landscape from the GX7 that wasn't under the best light. From normal viewing distance, over three feet, it's totally fine.
During my last journey to Serbia, I shot side-by-side,D800 and GX7 at similar high ISO and lighting. The GX7 isn't a D800 nor close to the low-light quality but the GX7 came through fine. Ask yourself, will you be showing your photos from both systems side-by-side in a gallery and will most others viewers have an issue with your photos? Will anyone care about the different looks and image quality in the end?
Since I'm aging and getting tired of packing a full D800 system with all the fixings tipping the scale at 18KG vs. 6KG with my GX7 system, I'm perfectly happy having a different look and lower IQ at high ISO for the images that I once only dreamed of capturing. Everything is a trade-off but worth it when the ink hits the paper.